In the transmission on a data network, for example organized in frames, an important role is played by the strategies of access to the communication medium. These strategies aim at preventing—or else reducing—possible situations of collision that are likely to cause the loss of messages and of the information contained therein.
Devices such as modems, transceivers, and the like, which can be used for transmitting data over a physical medium (i.e., over a channel) in communication networks, can use various hardware systems for checking whether there is a transmission in progress (namely, for detecting the condition of “band in use”). Various solutions enable regulation of operation of the devices with procedures (for example, at a firmware level) aimed at implementing strategies of access to the resource represented by the physical medium or channel. These strategies are referred to as Carrier-Sense Multiple Access (CSMA), and fall within two basic categories: in one case aimed at avoiding collisions (also referred to as Collision Avoid or CA) and in the other case aimed at detecting collisions (Collision Detect—CD).
Power-line modem devices such as the ST7580 use a Phase Shift Keying (PSK) modulation with a generic frame comprising a preamble part containing synchronization information for the stream, modulation, and payload used for decoding the frame itself.
The Power-Line Modem devices are able to supply information on channel status (for example, free or occupied) only after decoding a preamble. During decoding of the preamble, the power-line modem devices are not able to supply information on the channel status. This delay of signalling of the “band in use” penalizes the performance of a classic CSMA/CA procedure.
Another problem is linked to the overall system architecture, which may comprise a microcontroller (e.g., STM32) and a Power-Line Modem (e.g., ST7580) connected via serial-communication peripherals, the microcontroller managing the data flows from and to the modem. The external control introduces a delay due to serial transmissions, the delay being proportional to the size of the packet exchanged.
In various solutions, the delay introduced by the serial communication between the microcontroller and the modem causes an increase of the interval in which the transmission channel is effectively “booked” by a transmission, and the devices belonging to the network are unable to verify the effective channel status.